I have a django app that uses django-authopenid as the sole registration method. I have registration in my installed apps, which django-authopenid uses. An ideal solution would allow me to run arbitrary code on the user object when they register. I can't directly modify the code for django-authopenis or registration.
Let me know if I need to add any more details.
On models.py you could bind the post_save signal:
from django.contrib.auth.models import User, Group
from django.db.models.signals import post_save
def default_group(sender, instance, created, **kwargs):
if created:
instance.groups.add(Group.objects.get(name='your default group name'))
post_save.connect(default_group, sender=User)
If in doubt, read the signals documentation.